This invention pertains generally to multicolor electrographic printing devices. In particular, the present invention is an automated thermal lamination system for transferring a toned image from an electrostatic surface to a print medium.
Typically, to produce a multicolor print a photoconductive member of the electrographic printer is first charged to a uniform potential to sensitize its imaging surface. The charged surface of the photoconductive member is exposed to an image that is to be reproduced as a multicolor print. This procedure allows the photoconductive member to record an electrostatic latent image corresponding to the informational areas contained within the image.
To form a multicolor print, successive images are developed with different colored liquid toners supplied from corresponding toner developing modules. The color of the liquid toner in the particular developing module corresponds to the substractive primary of the color of the optical filter. Electrographic printing is normally done with yellow, cyan and magenta liquid toners. Usually the electrographic printer also includes a developing module having black liquid toner since it is required in virtually all commercial color printing applications. The different colored developed images are transferred from the photoconductive member to a print medium in superimposed registration with one another. A half tone screen is sometimes used to expose the images to create multisized dots that produce varying color tones needed to duplicate the original document. Heat is usually applied to permanently fuse the image to the print medium to form a completed multicolor print.
Numerous processes have been proposed for transferring an image from an electrostatic surface to a print medium. In some arrangements, the image is borne on a rotating drum and transferred directly to the print medium. Such an arrangement is illustrated, for example, in Ariyama et al. U.S. Pat. No. 4,640,605. In the process of this Ariyama et al. patent, a photosensitive drum serves as an image carrier. An optical system forms the electrostatic latent image on the drum, a development device develops the image into a visible image on the drum and a sheet feeder feeds an image transfer sheet between the drum and a charger for transferring the visible image from the drum to the image transfer sheet. The sheet is then separated from the drum and the photosensitive drum surface is cleaned for reuse.
Clemens U.S. Pat. No. 4,066,802 discloses the transfer of a multicolored toned image from a photoconductor, first to an adhesive carrier sheet, and then to a receptor sheet. The second transfer step involves the application of heat and pressure with a "polymeric or plasticized sheet" between the image on the carrier sheet and the receptor sheet surface. A temporary composite multicolored image is produced on the drum by overlaying on the surface a succession of liquid toned images of differing colors produced by separate charging, exposing and toning procedures. The conductor surface is addressed with an optical image or a chart retaining surface addressed with electrical styli. To produced the desired electrostatic latent image to be transferred.
Simm U.S. Pat. No. 4,383,019 discloses a process for transferring an image to a print medium to form a multicolor print. In this process, color separation images in red, green and blue are projected onto the surfaces of three metal drums. The surface of each metal drum is coated with a photoconductor which records the corresponding charged image. The charged image obtained for each color separation is continuously copied onto an image carrier which is moved past the drums. Immediately after the transfer of each image from a drum, the recopied charged image is transported by the continuously moving image carrier past a respective development apparatus wherein the charged images are developed in complimentary colors. The final fullcolor image is thus obtained by applying the partial charged images from each drum above one another on the image carrier, in correct registration. The image carrier is taken from a supply roll and transported mechanically over the metal drums. After the final color image has been applied on the image carrier, the image carrier travels with the image through a drying station. In a nip formed between a carrier drive drum and an idler drum, the transparent image carrier is backed with a white support layer and the toned image is fixed in the interface between the carrier and the support layer. The material used for the support layer is a self-adhesive white paper board which is taken from a continuous roll and pressed to the image carrier by an adhesive layer on the support layer. Before the support layer is applied to the carrier, however, a protective film covering the adhesive layer on the support layer is removed to expose the adhesive layer.
There is a continuing need for a process for efficiently and reliably transferring an image from an electrostatic member to a print medium. Current electrographic print arrangements are not reliable in their alignment of the transfer medium with respect to the carrier for the image, and often require special handling techniques or produce an end product which is aesthetically undesirable and requires further processing. In addition, prior electrographic printers have not been as efficient and compact as desired, nor have such printers been versatile enough to provide an end product which is suitable for all preprinting purposes. There is a continuing need for image transfer processes that can produce colorfast and smudge-free multicolor prints on a variety of proof paper substrates in a continuous and automated manner.